Atrioventricular septal defect overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Atrioventricular septal defect (AVSD), previously known as “common atrioventricular canal” (CAVC) or “endocardial cushion defect”, is a congenital heart defect characterized by the deficiency in development of the atrioventricular septum of the heart. It is caused by an abnormal fusion of the superior and inferior endocardial cushions with the mid-portion of the atrial septum and the muscular portion of the ventricular septum. The malformation results in a hole in the heart between the mitral and triscupid valves. This lack of separation can cause hemodynamic complications.

AVSD is classified as either complete, partial, or intermediate/transitional. Classification is based on the extent of loss of separation between the chambers of the heart. In partial AVSD, there is a defect in the primum or inferior part of the atrial septum but no direct intraventricular communication (ostium primum defect). In complete AVSD, there is a large ventricular component beneath either or both the superior or inferior bridging leaflets of the AV valve. In intermediate or transitional AVSD, the leaflets of the common AV valve are stuck to the ventricular septum causing a division of the two valves and resulting in a marginal sized hole between the ventricle. Transitional AVSDs are similar to partial AVSDs in behavior but visually appear more like a complete AVSD.

AVSDs can result in significant changes in hemodynamics. A defect in the septum can result in blood freely traveling from the left side of the heart to the right side of the heart resulting in mixing of oxygenated and deoxygenated blood. This mixed blood is pumped back to the lungs and causes an increase in blood volume in the lungs resulting in hypertension, cardiomegaly, and damage to the blood vessels. A high pulmonary pressure can result in a pulmonary edema

AVSDs account for approximately 5% of all congenital heart diseases. It is most commonly associated with patients with Down syndrome (trisomy 21) or heterotaxy syndromes.^[1] 45% of children with Down syndrome have some form of congenital heart disease. Of these, 35–40% have AV septal defects.^[2]

Most infants are largely asymptomatic and may only exhibit signs of failure to thrive. A clinical diagnosis often occurs based on the presence of a heart murmur and can be detected at any time, from fetal development to later in life. A fetal echocardiogram can detect the presence of a murmur during prenatal care. A cardiac catheterization can also used for diagnosis.

Surgical therapy is the most reliable method of treatment. An open heart surgery will separate the mitral and triscuspid valve and close the atrial and ventricular septal defects. Surgical therapy is not advised until a child is old enough to undergo surgery. A pulmonary artery banding surgery may be used to delay the necessity for surgery.

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